1. Field of the Invention
This invention relates to 3'-terminus modified nucleic acids including DNA and RNA, and methods for modifying 3'-termini of nucleic acid compounds.
2. Description of the Related Art
Labeling RNA 3'-termini is important for studies of gene regulation at RNA level and RNA biological function in vitro or in vivo, and for clinical test and research. There are two commonly used methods for end-labeling RNA: 3'-labeling with 3',5'-[5'-.sup.32 P]-pCp and T4 RNA ligase (England, et. al., Nature, 275:560-561, 1978; Uhlenbeck, et. al., The Enzymes, Vol. XV:31-58, 1982), and 3'-labeling with [.alpha.-.sup.32 P]-cordycepin 5'-triphosphate (CoTP or 3'-deoxy-ATP) and poly(A) polymerase (Linger, et. al., Nucleic Acids Res., 21:2917-2920, 1993; Edmonds, et. al., The Enzymes, Vol. XV:217-239, 1982). The 3'-labeling methods are less satisfactory. Labeling with T4 RNA ligase requires high concentrations of pCp and enzyme, and is less efficient at labeling long RNAs (Linger, et. al., Nucleic Acids Res., 21:2917-2920, 1993). Poly(A) polymerase labels short RNAs poorly (Linger, et. al., Nucleic Acids Res., 21:2917-2920,1993) and also requires a high concentration of [.alpha.-.sup.32 P]-CoTP for optimal incorporation (Beltz, et. al., Fed. Proc., 41:1450-1455,1982).